This invention relates to a gas turbine engine compressor assembly.
It is well known in the field of gas turbine engines to utilise a device known as a diffuser in order to reduce the velocity of a fluid flow exhausted from a compressor and thereby provide a corresponding increase in its pressure. Diffusers are located at the compressor outlet and typically consist of a duct which progressively increases in cross-sectional area in the direction of fluid flow or alternatively fixed vanes which define passages of progressively increasing cross-sectional area. The present invention is relevant to gas turbine engine compressor assemblies which incorporate either of these types of diffuser.
The diffuser of a gas turbine engine compressor assembly is usually designed so that it is most efficient in its operation when the gas turbine engine in which it is situated is operating under full power or near full power conditions. If the gas turbine engine is called upon to operate at lower levels of power, the efficiency of the diffuser falls and so in turn does the efficiency of the gas turbine engine. Ideally the velocity of the fluid flow exhausting from the diffuser should remain the same irrespective of whether the gas turbine engine is operating at full power or at lower levels of power. This can be achieved by mechanically varying the cross-sectional area of the diffuser. However difficulties associated with the mixing of the fluid flow through the diffuser can occur and in turn lead to local velocity variations in the fluid flow exhausted from the diffuser. Such local velocity variations are looked upon as being highly undesirable in view of the efficiency losses which they bring about in the operation of the gas turbine engine.